Heat / Cooling issue

[catmandu]

I bet someone can pinpoint this problem:

2000 4 cyl. and you start the car with the temp in the mid 20's it will rev to 1800 or so. Engine heats up normally, mid range on the coolant gauge. But cold air out of the heat ducts. Engine settles back to 800 rpm, heat air stays cold after 5 minutes or so. Give it some throttle in hopes of getting some heat, engine temp starts to climb towards overheat, but air out of heat ducts stays cold. Then all of a sudden, engine temp drops back to mid range, and finally you get hot air out of the ducts.

Thermostat? Heater control valve? Heater core? Aliens in the coolant?

[Chris Crash]

Sounds like t-stat is sticking a bit. I would just change it and flush the cooling system, it's cheap enough why not?

[Maim Menu]

Your thermostat is probably sticked shut and needs a lot of pressure to open and let water through wich would explain why temp has to go up above middle before cooling back down.

I think Chris Crash is on the money with that one.